Microtomes are generally well-known and are typically used in biomedical experiments to prepare thin slices of tissue that can then be subjected to microscopic studies. The tissue to be sliced is often embedded in paraffin or is hardened by freezing so that it can be sliced as thinly as possible, typically through the use of a microtome. Live tissues and freshly fixed tissues are typically too soft for this type of cutting and it is thus difficult to obtain thin slices of such live tissues and freshly fixed tissues. One attempted solution has been the provision of a vibrating blade microtome in which the cutting blade has been vibrated horizontally with respect to the typically vertical or perpendicular movement of the cutting blade edge. Such vibrating microtomes are specifically intended to cut soft tissue slices without the need for tissue embedding or freezing. The horizontal oscillation of the blade, or its oscillation is a direction which is generally parallel to the longitudinal axis of the cutting edge, is provided as a high frequency vibration that has been more effective in slicing soft tissue samples than were prior cut devices. The resultant slices, cut by the vibrating microtomes, have had better slice quality than have slices cut by direct blade chopping.
In all current vibrating microtomes, the blade vibrates generally parallel with respect to the longitudinal axis of the cutting blade. Typically this means that the blade vibrates in a generally horizontal, side to side direction, at a high frequency. An amplitude of such a vibrating stroke must be at least 0.6 mm. If the stroke amplitude is less than this amount, the blade will not cut through the live tissue. Instead, the live tissue or the freshly fixed specimen will merely be compressed and will push back against the horizontally vibrating blade.
Vibrating microtomes have been noted recently as having undesirable vibrations of the cutting blade in the Z—-axis direction; i.e. the direction perpendicular to both the X-axis blade vibration direction and the Y-axis cutting direction. Efforts have been made in prior vibrating microtomes to reduce this Z—-axis movement of the cutting blade using a so-called “zero —” technique. While the blade movement is most often tested and quantified in test conditions, during vibrating of the blade but without cutting a tissue slice, the Z—-axis movement or vibration of the cutting blade in operating conditions has been largely ignored.
Double edged razor blades are widely used in vibrating microtomes for cutting tissue slices. Such a razor blade is broken or separated into two single edge blade parts by being severed or snapped along its longitudinal axis prior to use. The now half blade, with its single cutting edge is clamped, generally at its middle, along its longitudinal axis in the blade holder of a currently available vibrating microtome and is used to cut tissue slices. The thin razor blade is apt to be bent or deflected relative to the blade holder, particularly in the portion of the blade that is unsupported by the blade holder of the vibrating microtome. The razor blade is typically mounted on the blade holder and is inclined at an angle of 15-35 degrees, with respect to the surface of the tissue specimen. During slicing of the specimen, the specimen will itself tend to pull and to bend the blade toward the specimen. Such a bending of the blade, during slicing of the specimens, causes the formation of chatter marks in the cut or sliced specimen because of blade bending, or chatter, in the Z—-axis direction. Resistance of the tissue specimen to being sliced, and the inherent thin blade structure, together with its being mounted in a somewhat flexible fashion, all contribute to flexure of the blade in the Z—-axis and to the resultant formation of tissue damage by the infliction of chatter marks on the surface of the cut tissue specimens.
In current vibrating machines, the edge of the cutting blade vibrates on a horizontal cutting plane. Such a vibrating motion requires a long vibrating arm so that the cutting blade will be located in the middle of the tissue bath container. This relatively long vibrating arm is heavy and is difficult to support so that it will be able to vibrate at the desired speed but will not wobble.
In U.S. Pat. No. 7,146,895, to Kong et al., the applicants in the subject application, there is disclosed a sliding blade microtome. As described in that patent, the disclosure of which is expressly incorporated herein by reference, a diagonally sliding cutting blade is usable to slice thin specimens of live or dead tissue, which specimens have been embedded in a gel and have been extended from the open end of a specimen-holding syringe, by the use of a sliding blade microtome machine. The sliding blade machine disclosed in this prior Kong patent can cut soft tissue such as brain cerebrum into slices. However, this prior device still has several limitations. A first of these is that in connection with high fiber containing tissue, which thus tends to be difficult to cut, such as brain stem or cerebellum, direct sliding cannot cut through the tough tissue thus resulting in low quality tissue slices. Also, the thinnest slices that can be cut with the sliding blade machine described in the above-identified prior Kong patent have a thickness of about 70 to 80 μm. This thickness of cut precludes the sliding blade machine from being used in histology studies which typically require slice thicknesses between 10 and 40 μm.
It will thus be seen that a need exists for a device for cutting fresh tissue slices and for a method of using such a device that overcomes the limitations of the presently existing procedures and apparatus. The method and device for cutting fresh tissue slices in accordance with the present invention provides such a device and method and is a substantial advance in the art.